Red-backed Shrikes (Lanius collurio) adjust the mobbing intensity, but not mobbing frequency, by assessing the potential threat to themselves from different predators


Martin Strnad, Michal Němec, Petr Veselý, Roman Fuchs


We studied the ability to adjust nest defence to the potential threat to defending adults and their nests in the Red-backed Shrike. We presented mounts of two raptor species which predate on adult birds (Eurasian Sparrowhawk, Common Kestrel; differing in the proportion of adult passerines in their diets), and two species of nest predators (Common Magpie, Eurasian Jay; differing in the proportion of bird eggs and nestlings in their diets). A mounted Feral Pigeon was used as a control. Shrikes regularly mobbed the Sparrowhawk, Kestrel and Jay, but not Magpie or Pigeon. The mobbing frequency, in terms of the number of mobbing events per 20 min, did not differ among the three regularly-mobbed predators. If shrikes tried to chase the predator away, they did not adjust the mobbing frequency to the level of threat to the nest. The proportion of mobbing events with physical contact (mobbing hazardousness) declined from the most mobbed Jay to the Kestrel, and to the Sparrowhawk, which was considered most dangerous. Apparently the Red-backed Shrikes adjusted the mobbing hazardousness by assessing the potential threat to themselves. Our results show the importance of a differentiation between mobbing hazardousness and mobbing frequency in the study of nest-defence behaviour.

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